Storage media, including magnetic media such as hard disk drives, include defects that result from manufacturing (e.g., present in a brand new or virgin disk drive) and/or from the environment or usage over time. At a defect location, data cannot be reliably written to the media. For example, when reading data at a defect location, an overly strong signal (e.g., that saturates a circuit), a weak signal, or no signal at all may be read. Defect scanners are used to create a map of defect locations so that these locations are not written to or read from. Typically, a defect scan is performed on a new disk drive and a map is obtained in this way.
Current defect scanning techniques are inefficient. Typical defect maps have limited resolution and can only indicate defect locations down to the sector level. In other words, typical defect scanners are only able to determine in which sector a defect is located. Even though a defect region may be much smaller than a sector, the entire sector is unused, which is inefficient. In addition, typical defect scanners require peak samples (e.g., a local maximum) as input. This means that the signal timing must first be acquired (i.e., so that the location of the peaks is known), which requires a timing loop and takes additional time. In addition, defects that occur before the timing is acquired (e.g., in a preamble or beginning portion) are not detected. As such, improved defect detection techniques would be useful.